drm/exynos: Move dp training into mode_set

drm/exynos: Move dp training into mode_set

Move the DP link training from the interrupt worker to the mode_set
callback.

BUG=chrome-os-partner:17557
TEST=Tested on snow, no regressions noted

Change-Id: I06fecce43500e4a2b64eda4aca18c889a811b1ed
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/43924
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>